Screw bosses for blow-molded structures

ABSTRACT

A screw boss for blow-molded structures, such as portable tables and chairs, allows various components to be securely attached to the blow-molded structure. For example, the screw boss may allow support legs to be securely fastened to a blow-molded table top. The screw boss is integrally formed in an outer surface of the blow-molded structure and it includes a receiving portion that is sized and configured to receive a fastener such as a screw. Preferably, the fastener has threads that threadably engage the inner surface of the receiving portion to provide for secure attachment of the fastener to the blow-molded structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to and the benefit of U.S. provisional patent application serial No. 60/285,305, entitled “Method and Apparatus for Creating Screw Bosses in a Blow-Molded Workpiece,” filed on Apr. 20, 2001, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to blow-molded structures. In particular, the present invention relates to screw bosses that can be used to attach and secure a variety of components to blow-molded structures.

[0004] 2. Description of Related Art

[0005] The use of plastic today reaches into nearly every facet of everyday living. Ease of manufacturing, strength, and durability are qualities that make plastic a popular choice for manufacturing a wide variety of products. For example, products such as table tops, park benches, chair backs and seats, and basketball backboards may be constructed from plastic.

[0006] Blow-molding is one of many methods for producing plastic products. Structures produced by blow-molding are substantially hollow, which makes this process a preferred method for manufacturing products that are lightweight yet durable. Blow molding is also a relatively simple process, which further increases its popularity.

[0007] In order to construct conventional blow-molded plastic structures, an extruded parison, comprising a hollow tube of heated plastic, is positioned between two opposing sides of a blow-molding press. The inner sides of the blow-molding press serve as the mold against which the blow-molded structure is formed. Once the parison is positioned inside the press, the two opposing sides of the press are closed. This closure clamps either or both ends of the parison to create an air-tight chamber or inner volume. A needle or air inlet is then inserted through the plastic parison wall and pressurized air or other gas is injected into the air-tight chamber. The air or gas causes the plastic parison to deform and engage the sides of the blow-molding press, which causes the plastic to take the shape of the mold. Once the plastic has been molded into the desired shape, the press is cooled and the structure, now substantially rigid, is removed from the press. The process may then be repeated using a new parison.

[0008] While blow-molding is an effective process for manufacturing plastic structures, it has several limitations and disadvantages. For instance, because blow-molded structures are hollow, thin-walled structures, it is difficult to use standard mechanical fasteners to attach components to blow-molded structures. In particular, the thin outer walls of blow-molded structures typically have a thickness of about {fraction (1/16)} inch to about ¼ inch and standard mechanical fasteners, such as screws, require a greater thickness for secure attachment. Specifically, because the threads of the screw only engage the thin outer wall, there is very little engagement between the screw threads and the blow-molded structure. As a result, there is not a secure engagement of the screw to the blow-molded structure and the screw can be easily loosened or torn out of the structure altogether. Accordingly, components attached to blow-molded structures by screws or other mechanical fasteners are prone to wobbling or complete separation from the structure. In the case of components serving as a support for the blow-molded structure, such as legs for a plastic blow-molded table top, the screws may not securely attach the legs to the table top and the table may collapse or fail.

[0009] In order to strengthen the engagement of screws to blow-molded structures, it is known to increase the outer wall thickness. Disadvantageously, it is very difficult to control the wall thickness in blow-molded structures. Thus, increasing the outer wall thickness may still not provide secure engagement of standard mechanical fasteners to blow-molded structures because sometimes the outer wall may have sufficient thickness while other times it may not. Additionally, the increased wall thickness increases costs, manufacturing time and weight of the structure. Further complicating this situation is the fact that some regions of the blow-molded product are thicker than others. Thus, a fastener that may engage the structure with sufficient strength in one region may not adequately hold in another region.

[0010] It is also known to construct blow-molded structures with outer walls that are substantially parallel and adjacent to one another. In this way, a fastener such as a bolt or a screw may pass through both walls of the blow-molded structure to more securely attach components to the structure. A nut is typically placed on the end of the bolt to tighten the connection. This approach, however, suffers from several drawbacks, including increased time and parts required to assemble the product, and the unsightly presence of the fastener on multiple surfaces of the blow-molded structure. Further, this type of fastening system may still be unable to prevent undesired loosening or removal of the bolt or screw because of the limited engagement of the threads with the thin outer walls and the bolt or screw can still be torn out of the thin outer walls.

[0011] Another known way to fasten components to blow-molded structures involves the use of hollow wall fasteners commonly used in dry wall anchoring. An enlarged hole is made in the wall of the blow-molded structure and a bolt with an attached anchoring device is inserted into the hollow interior of the blow-molded structure. Once inside the structure, the anchoring device, which may have toggle wings or an expandable collar, expands and engages the inner surface of the wall. The bolt is then tightened to securely attach the component to the structure. Disadvantageously, this known type of fastener requires a large hole be formed in the blow-molded structure, which increases costs and labor, and requires additional parts, which further increases costs and labor.

[0012] It is further known to attach a separate part to the blow-molded structure and a fastener is then threadably connected to that part to allow components to be attached to the blow-molded structure. For example, a hole could be formed in the blow-molded structure and an insert could then be inserted into the hole and attached to the structure. The insert includes a receptable that is sized and configured to receive the fastener. Disadvantageously, a hole must be formed or made in the blow-molded structure and the insert must be inserted and attached to the hole. This increases both costs and manufacturing time.

[0013] Additionally, it is known that an insert may be attached to the blow-molded structure during the manufacturing process. In particular, the insert is positioned on or proximate an inner mold surface of the blow-molding press and the plastic parison deforms around the insert during the blow-molding process. Protrusions disposed on the outer surface of the insert may help secure it to the blow-molded structure. The insert includes an opening with threads that are sized and configured to receive the fastener. Unfortunately, attaching the insert to the structure during the blow-molding process is very time consuming because an insert must be positioned proximate the inner surface of the mold before each blow-molding cycle. Additionally, this known fastening scheme requires multiple parts, which increases costs, and often requires specially manufactured inserts. Disadvantageously, the strength of the connection is dependent upon the engagement of the insert and the blow-molded structure. Thus, if the blow-molded plastic does not completely deform about the insert, then the insert may not be securely attached to the blow-molded structure. Further, because the protrusions of the insert may easily become disengaged from the blow-molded structure, the insert may not provide a secure engagement of the fastener to the structure.

SUMMARY OF THE INVENTION

[0014] A need therefore exists for an apparatus that allows fasteners to be securely attached to blow-molded structures, while eliminating the above described problems and disadvantages.

[0015] One aspect of the present invention is a screw boss that allows components to be securely attached to blow-molded structures. Advantageously, the screw boss is integrally formed in the blow-molded structure and it requires no additional parts or components to be attached to or formed in the structure. Thus, no inserts or other parts have to be attached to or formed in the blow-molded structure.

[0016] Another aspect is a screw boss that is formed in an outer surface of a blow-molded structure during the manufacturing process. The screw boss includes an opening and a receiving portion with an elongated cavity. The receiving portion extends inwardly into the blow-molded structure and it includes inner and outer surfaces. The receiving portion is sized and configured to receive a fastener such as a bolt or screw. Preferably, the receiving portion is sized and configured to threadably receive a fastener such as a screw wherein the inner diameter of the receiving portion is generally equal to or greater than the minor diameter of the screw and smaller than the major diameter of the screw.

[0017] A further aspect is integrally forming the screw boss in the plastic structure during the blow-molding process. Preferably, the blow-molding process includes a blow-molding press having two halves with molds disposed on their respective inner sides. The two mold halves cooperatively mate to form a mold cavity therein. An inwardly extending pin or projection is disposed on an inner surface of the mold where a screw boss is desired to be formed. A heated plastic parison is then placed in the mold cavity, the mold halves are mated, and the blow molding process is begun. During the process, the heated plastic is filled with gas such that the parison engages the inner sides of the mold cavity and it conforms to the shape of the mold halves. The heated plastic parison also deforms about and conforms to the shape of the projection disposed on the inner surface of the mold to form the screw boss. Once the blow-molded structure is cooled and removed from the press, the screw boss is integrally formed in the structure.

[0018] A still further aspect of the screw boss is it can have any suitable size and configuration depending, for example, upon the desired type of fastener to be connected to the structure. Advantageously, the projection attached to the mold press can be used to form screw bosses with different sizes and configurations. For example, the length, thickness and shape of the projection may vary according to the type of the screw boss to be formed.

[0019] A further aspect is the size and shape of the screw boss is preferably dependent upon the desired type of fastener to be connected to the blow-molded structure. For example, the screw boss can have an elongated receiving portion to receive an elongated fastener or a shorter receiving portion to receive a shorter fastener. Preferably, the length and inside diameter of the receiving portion are sized and configured such that the inner surface of the receiving portion engages at least a portion of the fastener. More preferably, the receiving portion has a length and inside diameter that is sized and configured to engage the threads of the fastener along all or a substantial length of the fastener. For example, the length of the receiving portion is preferably greater than twice the thickness of the outer wall of the blow-molded structure to allow the fastener to be securely attached to the structure. Advantageously, the engagement of the threads of the fastener with the receiving portion of the screw boss over an extended length greatly increases the strength of the connection between the fastener and the blow-molded structure.

[0020] Still another aspect is the thickness of the wall of the inwardly extending receiving portion of the screw boss is preferably sufficient to allow the threads of the fastener to bite into the wall without puncturing the wall. This provides for secure engagement of the fastener to the screw boss.

[0021] Another aspect is the screw bosses can be located in virtually any desired portion of the blow-molded structure. This allows fasteners and other components to be attached to virtually any desired portion of the blow-molded structure. The screw bosses, however, are preferably located a suitable distance away from structural support members such as support bars or reinforcing bars such that the structural support members do not lose any of their strength or rigidity.

[0022] A further aspect is the screw bosses are preferably formed in portions of the blow-molded structure that have a relatively thick outer surface. This allows the screw bosses to be formed in the blow-molded structure without creating an opening or stress point in the outer wall of the blow-molded structure.

[0023] Yet another aspect is the screw bosses are preferably located in portions of the blow-molded structure that have a stretch region sufficient to accommodate the forming of the screw boss during the manufacturing process. The stretch region allows the plastic to stretch while the screw boss is being formed without creating holes, unnecessary stress points or weaknesses in the outer surface of the structure. The proper stretch region is significant because the plastic in the stretch region deforms or stretches about the protrusion, which causes the thickness of the plastic outer wall to decrease. The site of the stretch region may vary according to the size of protrusion used to form the screw boss. Advantageously, forming the screw boss in an area that has a sufficient stretch region prevents the outer wall of the blow-molded structure and the wall forming the receiving portion of the screw boss from being insufficiently thick or from rupturing during the blow-molding process. Also, the placement of a screw boss too close to another structure feature, such as a structural rib or tack-off, may cause improper formation of the boss.

[0024] These and other aspects, features and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The appended drawings contain figures of preferred embodiments to further clarify the above and other aspects, advantages and features of the present invention. It will be appreciated that these drawings depict only preferred embodiments of the invention and are not intended to limits its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0026]FIG. 1A is a perspective view of an exemplary table with a table top constructed from blow-molded plastic and a pair of table legs attached to the table top, the table top includes screw bosses in accordance with a preferred embodiment of the present invention to allow the table legs to be securely attached to the table top;

[0027]FIG. 1B is a perspective view of a portion of the table shown in FIG. 1A, illustrating the underside of the table and the table legs attached to the table top by a plurality of screw bosses;

[0028]FIG. 2A is an enlarged perspective view of a screw boss in accordance with another preferred embodiment of the present invention;

[0029]FIG. 2B is a cross sectional side view of the screw boss shown in FIG. 2A taken along the line 2B-2B;

[0030]FIG. 3A is an enlarged perspective view of a screw boss in accordance with yet another preferred embodiment of the present invention;

[0031]FIG. 3B is a cross sectional side view of the screw boss shown in FIG. 3A taken along the line 3B-3B;

[0032]FIG. 4A is an enlarged side view of an exemplary fastener in the form of a screw that may be used in connection with the screw boss;

[0033]FIG. 4B is an enlarged perspective view of a screw boss in accordance with still another preferred embodiment of the present invention, illustrating the screw boss formed in an outer surface of a blow-molded structure and the screw shown in FIG. 4A attaching a component to the blow-molded structure via the screw boss;

[0034]FIG. 4C is a cross sectional side view of the screw boss shown in FIG. 4B taken along the line 4C-4C;

[0035]FIG. 5A is an enlarged side view on an exemplary projection attached to a blow-molding press and an exemplary plastic surface, illustrating the plastic surface before engagement with the projection during the blow-molding process;

[0036]FIG. 5B is a side view of the projection and plastic surface shown in FIG. 5A, illustrating the plastic surface initialing contacting the projection of the blow-molding press;

[0037]FIG. 5C is a side view of the projection and plastic surface shown in FIG. 5B, illustrating the plastic deforming about the projection of the blow-molding press;

[0038]FIG. 5D is a side view of the plastic surface shown in FIG. 5C, illustrating a preferred embodiment of the screw boss formed in the plastic surface with a closed end;

[0039]FIG. 5E is a side view of the plastic surface shown in FIG. 5C, illustrating another preferred embodiment of the screw boss formed in the plastic surface with an open end;

[0040]FIG. 6A is an enlarged side view of a preferred embodiment of a projection that may be used to form a screw boss;

[0041]FIG. 6B is an enlarged side view of another preferred embodiment of a projection that may be used to form a screw boss;

[0042]FIG. 6C is an enlarged side view of a yet another preferred embodiment of a projection that may be used to form a screw boss;

[0043]FIG. 6D is an enlarged side view of still another preferred embodiment of a projection that may be used to form a screw boss;

[0044]FIG. 7A is a top view of an exemplary fastener that may be used in connection with the screw boss;

[0045]FIG. 7B is a side view of the exemplary fastener shown in FIG. 7A;

[0046]FIG. 8A is a top view of another exemplary fastener that may be used in connection with the screw boss;

[0047]FIG. 8B is a side view of the exemplary fastener shown in FIG. 8A;

[0048]FIG. 9A is a top view of still another exemplary fastener than may be used in connection with the screw boss; and

[0049]FIG. 9B is a side view of the exemplary fastener shown in FIG. 9A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] The present invention is directed towards screw bosses formed in blow-molded structures such as tables and chairs. The principles of the present invention, however, are not limited to screw bosses for tables or chairs. It will be understood that, in light of the present disclosure, the screw bosses disclosed herein can be successfully used in connection with other types of furniture and other suitable structures.

[0051] Additionally, to assist in the description of the screw bosses, words such as top, bottom, front, rear, right and left are used to describe the accompanying figures. It will be appreciated, however, that the present invention can be located in a variety of desired positions—including various angles, sideways and even upside down. A detailed description of preferred embodiments of the screw boss now follows.

[0052] As shown in FIGS. 1A and 1B, a portable table 10 includes a plastic, blow-molded table top 12 and metal support legs 14. The table top 12 has a top surface 16, a bottom surface 18, and side surfaces 20. In general, blow molded tables are a popular choice because of their portability, low weight, and durability. These characteristics are possible in part because of the blow-molded nature of the table top 12.

[0053] As best seen in FIG. 1B, the support legs 14 are attached to the bottom surface 18 of the table top 12 via a plurality of brackets 22 and fasteners such as screws 24. Though obscured by the brackets 22, the screws 24 are securely attached to the table top 12 via screw bosses 30. Advantageously, the screw bosses 30 enable the table support legs 14 to be securely attached to the bottom surface 18 of the table top 12.

[0054] Note that for clarity the screw bosses 30 are shown in the accompanying figures and described in the accompanying text as being used to connect support legs 14 to the table top 12. It will be appreciated, however, that the screw bosses 30 can be used in connection with a variety of blow-molded structures and components, as may be required for a particular application. Additionally, the screw bosses 30 can be used with a wide variety of fasteners such as screw and bolts, and the screw bosses allow a wide variety of components and objects to be connected to blow-molded structures. Significantly, the screw bosses 30 described herein can be used in connection with any suitable type of blow-molded structures.

[0055]FIGS. 2A and 2B depict an embodiment of the screw boss 30 with an opening 32 and a receiving portion 34. The receiving portion 34 includes an end 36 disposed opposite the opening 32 and the receiving portion is generally defined by a wall 38 with an inner surface 40 and an outer surface 42. The screw boss 30 is preferably formed in the bottom surface 18 of the table top 12, but the screw boss could be located in any suitable location. The opening 32 of the screw boss 30 is desirably generally flush with the bottom surface 18 of the table top 12 and the receiving portion 34 extends generally inwardly into the hollow center section of the table top.

[0056] The opening 32 and the receiving portion 34 of the screw boss 30 are sized and configured to threadingly receive a fastener, such as the screw 24, in order to secure the attachment of the support legs 14 to the bottom surface 18 of the table top 12. One skilled in the art will appreciate that the opening 32 and the receiving portion 34 of the screw boss 30 may have any one of a variety of shapes according to the physical characteristics of the fastener that is to be received therein. In one aspect, and as best seen in FIG. 2B, the receiving portion 34 has a generally bullet shaped central cavity with a tapered end 36. Alternatively, the receiving portion 34 could have cylindrically or conically shape, for instance. A detailed discussion concerning the inter-relationship between the receiving portion 34 and the fastener, as well as the mating thereof, is given further below.

[0057] Reference is now made to FIGS. 3A and 3B, illustrating another embodiment of the screw boss 30. In this embodiment, the receiving portion 34 is disposed in the bottom surface 18 of the table top 12 and the receiving portion has a generally conical shaped configuration with a rounded end 36. In contrast to the screw boss shown in FIG. 2B, the end 36 of the receiving portion 34 engages another wall of the blow-molded structure. In particular, the end 36 of the receiving portion 34 preferably engages the top surface 16 of the blow-molded table top 12. The screw boss 30 of the type shown in FIG. 3B may be referred to as a “tacked” boss. The screw boss 30 of FIG. 2B, on the other hand, may be referred to as a “blind” boss in that it makes no contact with any other surface. This contact between the end 36 of the receiving portion 34 of the screw boss 30 and a surface such as the top surface 16 of the table top 12 may be incorporated into the design of the blow-molded structure to provide the screw boss and/or blow-molded structure with increased strength.

[0058] Reference is now made to FIGS. 4A, 4B, and 4C, which illustrate further details of the screw boss 30. FIG. 4A depicts various details of an exemplary fastener, such as a screw 50, which threadably engages the screw boss 30. It should be understood that the screw 50 of FIG. 4A is but one example of a threaded fastener that may be employed to engage the screw boss 30. Accordingly, it will be appreciated that other types and configurations of suitable fasteners may be used in connection with the screw boss 30 depending, for example, upon the type, size and intended use of the blow-molded structure. The screw 50 generally includes a head 52, a shaft 54, one or more threads 56, a minor diameter d₁, and a major diameter d₂. The head 52 of the screw 50 may include a washer-like extension 58 to facilitate engagement of the screw with another surface. It will be appreciated, for example, that the screw 50 may have a tapered shaft 54 and/or the threads 56 may have variable sizes and spacing. The shaft 54 and/or threads 56 may also have different diameters and thicknesses that vary, for example, along the length of the shaft. The size and configuration of the screw 50, however, is preferably complementary to the screw boss 30 to allow the screw to be securely attached to the blow-molded structure.

[0059]FIGS. 4B and 4C illustrate an embodiment of the screw boss 30 that may be used to secure the support legs 14 to the bottom surface 18 of the blow-molded table top 12. One skilled in the art will appreciate that this may be accomplished a variety of ways; thus the particular configuration shown in FIGS. 4B and 4C should be considered exemplary and not limiting of the present invention. In these figures, the screw boss 30, which is similar to that shown in FIG. 3B, is shown threadingly receiving the screw 50 in the receiving portion 34. A portion of the bracket 22 is interposed between the washer-like extension 58 of the screw 50 and the screw boss 30. The bracket 22, in turn, securely holds the support legs 14 in the desired position. In this way, the support legs 14 are securely attached to the table top 12, thereby enabling the combination to function as a table 10.

[0060] As best seen in FIG. 4C, the screw 50 is received within the screw boss 30 such that the threads 56 engage the inner surface 40 of the receiving portion 34. In particular, the screw 50 is inserted it a short distance into the receiving portion 34 and then it is rotated with a tool such as a screwdriver while applying a predetermined amount of downward force, as is well known in the art. In comparing FIG. 4B with FIG. 3B, note that the inner surface 40 of the receiving portion 34 is preferably not pre-threaded. Thus, the screw threads 56 bite into the inner surface 40 of the receiving portion 34 as the screw 50 is inserted into the screw boss 30 and the thread paths 59 are “cold formed” by the screw upon its insertion into the screw boss. It will be appreciated, however, that the receiving portion 34 of the screw boss 30 may be pre-threaded if so desired.

[0061] Advantageously, the size and configuration of the screw boss 30 and screw 50 are preferably correlated or matched to maximize the engagement between the two. Specifically, the length, thickness and diameter of the receiving portion 34 are preferably sized and configured to receive a particular type of fastener or screw. In particular, the screw preferably has a specified length, minor diameter d₁, and major diameter d₂ to be generally received within the receiving portion 34 of the screw boss 30 and to securely engage the inner surface 40 of the receiving portion.

[0062] Desirably, the length of the receiving portion 34 is generally equal to or greater than the length of the screw shaft 54 such that the threads 56 of the screw 50 engage the inner surface 40 of the screw boss 30. Significantly, because the threads 56 engage the inner surface 40 of the receiving portion 34 over an extended length, this allows secure engagement of the screw 50 to the screw boss 30. For example, the length of the receiving portion 34 may be at least twice the thickness of the out wall or twice the diameter of the screw 50 to allow for secure engagement of the screw to the screw boss 50. Preferably, the length of the receiving portion 34 is sufficient to receive the screw shaft 54 without having the tip of the screw puncture the end 36 of the receiving portion in a blind boss, as shown in FIG. 2A and 2B, or without having the screw tip puncture the second end of the receiving portion in a tacked boss, as shown in FIG. 4C. It will be appreciated, however, that the screw 50 and receiving portion 34 can have any suitable lengths depending upon, for example, the type of fastener or intended use of the blow-molded structure and the screw may protrude through one or more surfaces.

[0063] The inner diameter of the receiving portion 34 of the screw boss 30 is preferably slightly larger than or generally equal to the minor diameter d₁, of the screw, yet smaller than the major diameter d₂ of the screw. Such an arrangement is seen in FIG. 4C. This enables at least a portion of the threads 56 to bite into the inner wall 40 of the receiving portion 34 when the screw 50 is threadably engaged with the screw boss 30. At the same time, the thickness of the wall 38 of the receiving portion 34 should be sufficient to prevent the threads 56 from puncturing and extending through the outer surface 42 of the receiving portion because that may reduce the strength of the attachment between the screw 50 and the screw boss 30. It will be understood that when the screw boss 30 is tacked to another surface of the blow-molded structure, such as a table top 12, the tip of the screw 50 may protrude through the end 36 of the receiving portion and it may engage or protrude through the other surface.

[0064] During the manufacturing process of the screw boss 30, which is more fully described below, the thickness of the receiving portion 34 typically varies along the length of the receiving portion. In general, the thickest portion of the receiving portion 34 resides near the opening 32 and the thinnest portion is located at the end 36. Factors that may affect the wall thickness of the receiving portion 34 include the length of the receiving portion, the location of the screw boss 30 in the blow-molded structure, and the thickness of the outer walls of the blow-molded structure. Because the wall thickness of the screw boss 30 typically varies along the length of the receiving portion 34, this may impact whether a portion of the screw 50 extends through the screw boss.

[0065] As best seen in FIG. 4C, it is preferable that the receiving portion 34 engage the threads 56 of the screw 50 along substantially all or the entire length of the screw shaft 54 to maximize the engagement of the threads with the screw boss 30. Of course, engagement of the receiving portion 34 with the threads 56 along less than the entire length of the screw shaft 54 is also possible. Generally, however, it is desired that the threads 56 engage a length of the receiving portion 34 that is approximately equal to at least twice the average outer wall thickness of the blow-molded structure. This helps ensure sufficient screw thread 56 to screw boss 30 engagement to create a secure attachment of the screw 50 to the blow-molded structure.

[0066] Reference is now made to FIGS. 5A-5E, which depict a preferred method for integrally forming the screw boss 30 in the blow-molded structure, such as the table top 12. This method generally includes molten or heated thermoplastic material being fed into an extrusion die from a suitable supply source (not shown). The thermoplastic material is extruded from the extruder or die in the form of a hollow cylinder or parison 60 (a portion of which is shown in the accompanying figures) between a pair of mold sections 62 (only one of which is shown in the accompanying figures). The mold sections 62 are preferably movable into and out of engagement with the parison 60. In particular, the parison 60 is positioned between the mold sections 62 and the mold sections are then moved into engagement with the parison such that at least a portion of the parison is trapped between the mold sections. The mold sections 62 also pinch or close the parison 60 along one or more mold lines to form a generally sealed enclosure. Air or other suitable gases are introduced into the sealed enclosure to expand the thermoplastic material against the mold surfaces to form the molded structure. As known to those skilled in the art, the mold surfaces and molded plastic structures can be vented and cooling water can be circultated through the mold sections. This method forms a hollow, thin-walled structure such as a table top.

[0067] Advantageously, the screw boss 30 is formed directly in the blow-molded structure and the screw boss is formed entirely during the blow-molding process. This saves valuable manufacturing time because the screw boss 30 is integrally formed in the blow-molded structure and no additional parts or components have to be inserted, connected or attached to the blow-molded structure to form the screw boss. Again, while this method focuses on the formation of a screw boss 30 in a blow-molded table top 12, one skilled in the art will appreciate that the screw boss can be formed in any suitable structure and a variety of suitable methods to form the screw boss may be used.

[0068] The screw boss 30 is formed by a pin or projection 70 that is disposed on an inner surface 64 of the mold 62. The projection 70 is preferably disposed in a fixed or stationary position on the inner surface 64 of the mold 62, and the projection is preferably removably attached in order to allow projections with different sizes and configurations to be attached to the mold. This allows screw bosses 30 of different sizes and configurations to be formed. The projection 70 can also be retractable from the inner surface of the mold 62, if desired.

[0069] The shape and size of the projection 70 is preferably dependent upon the size and characteristics of the screw 50 that is intended to be connected to the screw boss 30. Additionally, the particular placement of the projection 70 on the inner surface of the mold is dependent upon the desired location of the screw boss 30 in the blow-molded structure. Preferably, the screw boss 30 is located a predetermined distant away from other features or components of the blow-molded structure, such as structural ribs or surface indentations, so that the screw boss does not interfere with these features. In addition, this distance separating the screw boss 30 from the other features or components avoids stretching of the plastic near these features and components, which may impact their strength and/or appearance.

[0070] As seen in FIGS. 6A-6D, the projection 70 includes a base 72 that is attached to the inner surface 64 of the mold 62, a main body portion 74 and a tip 76, and the projection can have a variety of different configurations to form various types of screw bosses 30 during the blow-molding process. These figures are representative of the variety of shapes that may comprise the projection 70, but one skilled in the art will understand that the projection can have any suitable configuration depending upon the intended configuration of the screw boss 30. For example, FIG. 6A shows a generally bullet-shaped projection 70 having a generally cylindrical body 74 and a smoothly pointed tip 76. The projection 70 of the type shown in FIG. 6A may be used to form the screw boss 30 shown in FIGS. 2A and 2B. FIG. 6B shows a projection 70 having a substantially cylindrical body 74 and a rounded tip 76 which may be used to form the screw boss 30 shown in FIGS. 3A-4B.

[0071]FIGS. 6C and 6D show other exemplary configurations of the projection 70. FIG. 6C shows a projection 70 comprising a substantially cylindrical body 74 and a frustoconical tip 76. FIG. 6D shows a projection 70 including a tapered body 74 and tip 76. Such a projection 70 may be used to form a screw boss 30 having a tapered receiving section 34 that is sized and configured to receive a screw 50 having a tapered shaft 54 and threads 56.

[0072] The projections 70 shown in FIGS. 6A-6D preferably have generally smooth outer surfaces to allow the projections to be easily removed from the molded structure and to prevent the plastic from snagging on a sharp edge during the blow-molding process. The generally smooth outer surfaces may also help prevent damage to the screw boss or molded structure when the structure is removed from the mold. It will be appreciated, however, that the projections may have one or more pointed surfaces or sharp edges depending, for example, upon desired configuration of the screw boss 30 to be formed in the blow-molded structure.

[0073] As seen in FIGS. 5A-5E, the process for making screw bosses 30 in a blow-molded structure begins by placing the heated plastic parison 60 in the mold cavity and the mating of the mold sections 62 causes the parison to be either positioned near the tip 76 of the projection 70, as shown in FIG. 5A, or the parison contacts the tip of the projection as shown in FIG. 5B. The parison 60 is then filled with air or gas which causes it to conform to the shape of the mold 62. In particular, the parison 60 engages and begins to deform about the projection 70 as shown in FIG. 5C. Once the parison 60 has been fully expanded against the inner surfaces of the mold, and formed about the projection 70, the mold is cooled and the blow-molded structure, such as the table top 12, is removed from the mold press. As shown in FIG. 5D, once the heated plastic parison is deformed about the projection 70 and the blow-molded structure is removed from the mold, the screw boss 30 is integrally formed in the blow-molded structure. As seen in the figure, the receiving portion 34 of the screw boss 30 is thicker near the opening 32 and thinner near the end 36. This thinning is due to the stretching of the heated plastic around the projection 70 during the manufacturing process. It is also evident from FIG. 5D that the portion of the outer wall of the blow-molded structure is thinner proximate the screw boss 30. This thinner area proximate the screw boss 30 is generally referred to as the stretch region. Significantly, the stretching and deforming of the plastic about the projection 70 causes both the thinning of the plastic near the end 36 of the screw boss and the thinning of the outer wall of the structure near the screw boss. For this reason it is desirable to choose a location for the such as structural ribs and tack offs, in order to protect the plastic surface of the blow-molded structure from excessive stretching or weakening.

[0074]FIG. 5E illustrates that the end 36 of the screw boss 30 can include an opening 78. The opening 78 is generally undesirable because it may allow foreign objects into the hollow center portion of the blow-molded structure and it may provide less surface area for the threads 56 of the screw 50 to engage. The opening 78 is typically the result of excessive stretching of the heated plastic caused either by an excessively large projection 70, or by the selection of a screw boss location that is either too close to other blow-molded features or the outer wall of the structure was too thin. The screw boss 30 with the opening 78 may still be utilized to threadingly receive a fastener in secure engagement with the blow-molded structure and it may be preferred in some instances.

[0075] Reference is now made to FIGS. 7A-8B, wherein various possible configurations of fasteners that my be used with suitable screw bosses 30 are shown. As mentioned above, the size and shape of a particular screw boss preferably corresponds to the size and shape of the fastener that is received by it such that a secure connection between the two is achieved. To the extent that a variety of screw shapes and sizes may be used to secure components to blow-molded structures, the particular size configurations of the screw bosses 30 are equally as diverse. It should be understood, therefore, that the types of fasteners that may be used with the screw bosses 30 are in no way limited to those shown in these figures.

[0076]FIGS. 7A and 7B show top and side views, respectively, of a screw 80 having a tapered shaft 82 and threads 84. A screw 80 of this type would be complementarily received by a screw boss 30 formed by the tapered projection 70 shown in FIG. 6D, for example.

[0077]FIGS. 8A and 8B show top and side views, respectively, of a screw 90 including a head 92, a tapered shaft 94 and threads 96. The head 92 includes a washer-like extension 98, a raised key portion 100, and a torx-type inset 102. The raised key portion 100 allows the head 92 of the screw 90 to be received into a key hole-type fitting (not shown) disposed in a component to be attached to the blow-molded structure. In the table top 12, for example, the shaft 94 and threads 96 of the screw 90 shown in FIGS. 8A and 8B could threadingly engage the screw boss 30 disposed in the table top 12, while the raised key portion 100 could engage a key-hole fitting disposed in the support legs 14. Because the key/keyhole engagement is typically hidden from view once engaged, it is often used where it is desirable to hide the screw 90.

[0078] One skilled in the art will appreciate that other threaded fasteners may be alternatively used with the screw boss 30 while preserving its functionality. For instance, FIGS. 9A and 9B are top and side views, respectively, of an insert 110 that may be threadingly connected to the screw boss 30. The insert 110 includes a head 112 that is integrated into the top of the shaft 114. The integrated head 112 includes a female engagement 116 that accepts a tool such as an Allen wrench, and a threaded interior core 118 that may receive a screw therein. The insert further includes a tapered body 120 and segmented threads 122 that allow the insert 110 to threadingly engage the screw boss 30. In use, the insert 110, being threadingly engaged with the screw boss 30, includes a screw disposed within the threaded interior core 118. The screw may be used to connect a component to the blow-molded structure. Accordingly, the above discussion makes clear that a variety of threaded fasteners may be adapted for use with the present screw boss 30.

[0079] Although the invention has been described in connection with certain preferred embodiments, other embodiments apparent to those of ordinary skill in the art are also within the scope of the invention. Accordingly, the described embodiments are to be considered in all respects only as illustrative and not restrictive, and the scope of the invention is intended to be defined only by the appended claims. It will also be understood that the principles of the present invention can be applied to other types of structures and not only blow-molded tables and chairs. 

What is claimed is:
 1. An apparatus that allows a threaded fastener to be threadably connected to a blow-molded structure, the apparatus comprising: an outer surface of the blow-molded structure, the outer surface having a thickness; and a screw boss integrally formed in the outer wall surface of the blow-molded structure as part of a unitary structure, the screw boss comprising: an opening in the outer surface of the blow-molded structure; and a receiving portion inwardly extending into the blow-molded structure from the opening, the receiving portion having an inside diameter that is sized and configured to threadably receive the fastener, the receiving portion having a length generally equal to or greater than twice the thickness of the outer wall of the blow-molded structure.
 2. The apparatus as in claim 1, wherein the extended length of the receiving portion allows one or more threads of the threaded fastener to engage the screw boss over an extended length to securely attach the fastener to the blow-molded structure.
 3. The apparatus as in claim 1, wherein the blow-molded structure comprises a table top.
 4. The apparatus as in claim 1, further comprising a wall generally disposed opposite the opening, the wall substantially enclosing the receiving portion of the screw boss.
 5. The apparatus as in claim 4, wherein the wall engages another surface of the blow-molded structure.
 6. The apparatus as in claim 5, wherein the blow-molded structure is a table top and the opening to the receiving portion of the screw boss is disposed in a lower surface of the table top and the wall engages an upper surface of the table top.
 7. The apparatus as in claim 1, further comprising a second opening generally disposed opposite the opening in the outer surface of the blow-molded structure.
 8. The apparatus as in claim 1, wherein the screw boss is generally disposed in a stretch region in the blow-molded structure.
 9. The apparatus as in claim 8, wherein the stretch region is generally located to minimize or eliminate interference of the screw boss with other features of the blow-molded structure.
 10. The apparatus as in claim 1, further comprising an inner diameter of the receiving portion, the inner diameter being generally equal to or slightly greater than a minor diameter of the threaded fastener to allow the threaded fastener to be readily received within the receiving portion of the screw boss.
 11. The apparatus as in claim 1, further comprising an inner diameter of the receiving portion, the inner diameter being generally smaller than a major diameter of the threaded fastener to allow the threaded fastener to be securely received within the receiving portion of the screw boss.
 12. A method of manufacturing an apparatus that allows a threaded fastener to be threadably connected to a blow-molded structure, the method comprising the steps of: forming an outer surface of the blow-molded structure, the outer surface having a thickness; and forming an integral screw boss in the outer wall surface of the blow-molded structure as part of a unitary structure, the screw boss comprising: an opening in the outer surface of the blow-molded structure; and a receiving portion inwardly extending into the blow-molded structure from the opening, the receiving portion having an inside diameter that is sized and configured to threadably receive the fastener, the receiving portion having a length generally equal to or great than twice the thickness of the outer wall of the blow-molded structure.
 13. The method as in claim 12, wherein the extended length of the receiving portion allows one or more threads of the threaded fastener to engage the screw boss over an extended length to securely attach the fastener to the blow-molded structure.
 14. The method as in claim 12, wherein the blow-molded structure comprises a table top.
 15. The method as in claim 12, further comprising forming a wall generally disposed opposite the opening, the wall substantially enclosing the receiving portion of the screw boss.
 16. The method as in claim 15, wherein the wall engages another surface of the blow-molded structure.
 17. The method as in claim 16, wherein the blow-molded structure is a table top and the opening to the receiving portion of the screw boss is disposed in a lower surface of the table top and the wall engages an upper surface of the table top.
 18. The method as in claim 12, further comprising forming a second opening generally disposed opposite the opening in the outer surface of the blow-molded structure.
 19. The method as in claim 12, wherein the screw boss is generally disposed in a stretch region in the blow-molded structure.
 20. The method as in claim 19, wherein the stretch region is generally located to minimize or eliminate interference of the screw boss with other features of the blow-molded structure.
 21. The method as in claim 12, further comprising forming the receiving portion of the screw boss with an inner diameter that is generally equal to or slightly greater than a minor diameter of the threaded fastener to allow the threaded fastener to be readily received within the receiving portion of the screw boss.
 22. The method as in claim 12, further comprising forming the receiving portion of the screw boss with an inner diameter that is generally smaller than a major diameter of the threaded fastener to allow the threaded fastener to be securely received within the receiving portion of the screw boss.
 23. An attachment system for use in securing one or more components to a blow-molded structure, the attachment system comprising: a fastener; a surface of the blow-molded structure having a thickness; and a screw boss integrally formed in the blow-molded structure as part of a unitary structure, the screw boss comprising: an opening in the surface of the blow-molded structure; and a receiving portion aligned with the opening in the surface of the blow-molded structure, the receiving portion having an inside diameter that is sized and configured to receive the fastener, the receiving portion having a length generally equal to or great than twice the thickness of the surface of the blow-molded structure.
 24. The attachment system as in claim 23, wherein the fastener is a threaded fastener with one or more threads disposed on an outer surface of the fastener.
 25. The attachment system as in claim 24, wherein the length of the receiving portion allows the one or more threads of the threaded fastener to engage the screw boss over an extended length to securely attach the fastener to the blow-molded structure.
 26. The attachment system as in claim 23, wherein the blow-molded structure comprises a table top.
 27. The attachment system as in claim 23, further comprising a wall generally disposed opposite the opening in the surface of the blow-molded structure, the wall substantially enclosing the receiving portion of the screw boss.
 28. The attachment system as in claim 27, wherein the wall engages another surface of the blow-molded structure.
 29. The attachment system as in claim 28, wherein the blow-molded structure is a table top and the opening in the surface of the blow-molded structure is disposed in a lower surface of the table top and the wall engages an upper surface of the table top.
 30. The attachment system as in claim 23, further comprising a second opening generally disposed opposite the opening in the surface of the blow-molded structure.
 31. The attachment system as in claim 23, wherein the screw boss is generally disposed in a stretch region in the blow-molded structure.
 32. The attachment system as in claim 31, wherein the stretch region is generally located to minimize or eliminate interference of the screw boss with other features of the blow-molded structure.
 33. The attachment system as in claim 23, further comprising an inner diameter of the receiving portion, the inner diameter being generally equal to or slightly greater than a minor diameter of the fastener to allow the fastener to be readily received within the receiving portion of the screw boss.
 34. The attachment system as in claim 23, further comprising one or more threads on an outer surface of the fastener and an inner diameter of the receiving portion, the inner diameter being generally smaller than a major diameter of the threaded fastener to allow the threaded fastener to be securely received within the receiving portion of the screw boss.
 35. The attachment system as in claim 23, wherein no portion of the fastener extends through the receiving portion of the screw boss.
 36. The attachment system as in claim 23, further comprising a wall generally disposed opposite the opening in the surface of the blow-molded structure, the wall engaging another surface of the blow-molded structure, the wall substantially enclosing the receiving portion of the screw boss.
 37. The attachment system as in claim 36, wherein the opening is formed in a lower surface of a table top and the wall engages an upper surface of the table top.
 38. A method of attaching a component to a blow-molded structure, the method comprising the steps of: forming an integral screw boss in an outer surface of the blow-molded structure, the screw boss including an opening in the outer surface of the blow-molded structure, the screw boss including a receiving portion aligned with the opening and having an inner diameter that is sized and configured to receive a threaded fastener; threadingly engaging the receiving portion of the screw boss with the threaded fastener, the threaded fastener having a minor diameter that is generally equal to or larger than the inner diameter of the receiving portion, the threaded fastener having a major diameter that is generally greater than the inner diameter of the receiving portion; and attaching the component to the blow-molded structure by the threaded fastener and the screw boss. 